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What is soft matter?

The states of matter extend well beyond atomic solids, liquids, and gases. Matter organizes itself at many different length scales and into many different forms, each distinguished by its microscopic symmetries and dynamics. There are, for instance, non-crystalline states with various degrees of order, like liquid crystals or copolymer phases, and there are some states—glasses and gels—that are disordered but which act like solids.

In fact, the properties of most of the materials we interact with on a daily basis result from disorder or heterogeneity at some length scale much larger than the atomic scale. For example, the atoms in a polymer network (like rubber) are organized into long chains that entangle to form a disordered mesh. The average mesh size is many times that of a single atom. Most of the properties of rubber can be described by simple models that ignore (or average out) the quantum mechanical interactions between atoms and treat the chains as macroscopic string-like particles. In general, we rarely have to understand the details of the interactions at the atomic scale in order to understand the properties of everyday materials. The success of simple models based on geometry and classical physics has led to a deeper and more generic understanding of condensed matter.

In our lab many of the experiments we do are with colloids, suspensions of particles that range from nanometers to micrometers in size. Like atoms, spherical colloidal particles can form crystals, liquids, glasses, and gels. But unlike the structures formed by atoms, the microstructures of colloidal phases are easily resolved—in situ and at room temperature—by optical microscopy, and the dynamics can be probed by relatively simple spectroscopic methods such as quasi-elastic light scattering. Because the interactions between particles are well understood, colloids have become model “atoms” for studying the formation and properties of condensed phases.

Some of the most difficult problems in condensed matter science today involve understanding how matter orders itself, or why it fails to do so, in three dimensions. A related problem in materials science and nanotechnology involves preparing materials that organize themselves in three dimensions. Experiments on colloidal phases could help resolve all of these issues. We're working to combine experimental techniques like scattering, diffraction, microscopy, and spectroscopy with new chemical and biochemical methods for preparing colloidal particles with tunable or anisotropic interactions. These new particles can act as more realistic model atoms and molecules. At the same time, particles with symmetries that are not observed in real atoms or molecules can act less like model atoms than designer atoms , which could become the foundation for building novel microstructured materials and new states of matter.

See the images at right for some examples of colloidal structures and materials. The publications page contains more information.